The Section on Clinical Brain Imaging has made a sustained effort to use positron emission tomography (PET) to help elucidate the neural mechanisms and pathophysiology of psychiatric disorders. The major focus of the Section over the past year has been directed at using PET to address questions about Attention-Deficit Hyperactivity Disorder (ADHD) in adult and teenage subjects. PET studies related to ADHD were conducted in three areas: Stimulant effects Studies were completed on the cerebral metabolic effects of chronic dextroamphetamine and methylphenidate treatment. Both stimulants appear to have modest metabolic effects in the brain while producing positive behavioral improvement. Studies on the cerebral metabolic effects of intravenous administration of dextroamphetamine were begun. Development PET studies on normal teenagers and those with ADHD are continuing. A new method, which allows minors to be scanned with minimal radiation exposure, is being employed and the initial description of the procedure has been published. In addition, teenagers with schizophrenia are being scanned by our Section using the new method. Thyroid Resistance Symptoms of ADHD are highly associated with generalized resistance to thyroid hormone, a disorder with a defined genetic defect. Preliminarily PET studies show impaired attention and reduced metabolism in the parietal lobe in adults with thyroid resistance. The Section has completed studies on scopolamine as a model for the memory impairment in Alzheimer~s Disease using PET. A clinical trial of the effectiveness of deprenyl in adults with ADHD was started. The Section is continuing work on the development of F-DOPA methodology, which is now extended to human subjects after initial work with nonhuman primates. Cyclofoxy PET scanning methodology is being applied to various patient groups. Using primate model, studies are continuing on metabolic effects of cocaine and fluphenazine. Finally, the Section is continuing its mission to train other research groups in the use of PET imaging technology and data analysis.